in extension.ts [219:231]
function createDiagnostic(severity: DiagnosticSeverity, markdownLink, lineText: TextLine, message): Diagnostic {
// Get the location of the text in the document
// based on position within the line of text it occurs in
let startPos = lineText.text.indexOf(markdownLink);
let endPos = startPos + markdownLink.length -1;
let start = new Position(lineText.lineNumber,startPos);
let end = new Position(lineText.lineNumber, endPos);
let range = new Range(start, end);
// Create the diagnostic object
let diag = new Diagnostic(range, message, severity);
// Return the diagnostic
return diag;
}